The human consumption of fats in various foodstuffs contributes significantly to obesity. High fat diets also contribute to various human diseases such as heart and coronary diseases. One method of reducing obesity and/or diseases such as heart and coronary diseases in the human population is to reduce the consumption of fat. In recent years, fat substitutes or low-calorie fats have attracted increasing attention as a method of reducing the fat and calorie content of foodstuffs. The objective is to provide edible fats with reduced absorption and digestive properties with minimal side effects and with acceptable taste and feel characteristics when incorporated into food compositions.
Transesterification reactions have been used to prepare saccharide polyesters with reduced absorption and digestive properties. Such transesterification reactions generally required high temperatures and/or toxic solvents (such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, and the like) and were not, therefore, generally suitable for the preparation of fat substitutes for use in food applications.
More recently, Meyer et al., U.S. Pat. No. 4,840,815 (issued Jun. 20, 1989), and Meyer et al., PCT Publication WO 92/03060 (published Mar. 5, 1992), provided a one-stage, solvent-free, low-temperature, low-pressure process for the preparation of saccharide fatty acid polyesters. The Meyer et al. process involves reacting a mixture of a lower acyl ester saccharide, a fatty acid lower alkyl ester, and an alkali metal catalyst at a reaction temperature of 100.degree. to 125.degree. C. while drawing a vacuum of less than about 15 torr over the reaction mixture. The saccharide fatty acid polyesters are reported to be formed via a transesterification reaction whereby at least a portion of the lower acyl ester groups on the starting saccharide are replaced with the fatty acid groups from the fatty acid lower alkyl ester. The transesterification catalysts employed were alkali metals, with sodium and potassium metals the most preferred. At the reaction temperature, the alkali metal catalysts were molten.
In addition to the transesterification catalysts used by Meyer et al. (i.e., elemental alkali metals), other basic transesterification catalysts are known for the preparation of saccharide fatty acid esters from the saccharides. Such basic transesterification catalysts include alkali metal carbonates, alkali metal hydroxides, and alkali metal alkoxides. None of the just-mentioned catalysts have been used in the Meyer et al. method.
Yamamoto et al., U.S. Pat. 4,611,055 (issued Sep. 9, 1986), report that the alkali metal carbonate and alkali metal hydroxide catalysts generally provide higher yields than the alkali metal alkoxide catalysts. Volpenhein, U.S. Pat. 4,517,360 (issued May 14, 1985), reports that the alkali metal carbonate catalysts provide increased yields and shorter reaction times than the alkali metal hydroxide and alkali metal alkoxide catalysts. These basic transesterification catalysts (i.e., alkali metal carbonates, hydroxides, and alkoxides) generally require higher reaction temperatures (on the order of 180.degree. C.) than the alkali metal catalysts of Meyer et al. Moreover, the transesterification methods and catalysts of Yamamoto et al. and Volpenhein generally require a fatty acid metal soap to insure a homogeneous reaction mixture. Such fatty acid metal soaps are not used or required in the Meyer et al. method. Mieth et al., German Patent 227,137 A1 (laid open Sep. 11, 1985), provides a method for preparing polyol-ester mixtures suitable for use as fat substitutes whereby saccharides are esterified or transesterified with short-chain carboxylic acid derivatives in the presence of a catalyst and then reacted with triglycerides having long-chain carboxylic acid derivatives (i.e., pig grease or hard rape fat) at a temperature of 120.degree. to 140.degree. C. The polyol-ester mixtures so produced can be subjected to further transesterification reactions at 100.degree. to 120.degree. C. using long-chain carboxylic acids or their esters as reagents. The catalysts used by Mieth et al. include phosphorous acid, alkali metals, alkali alkylates, and alkali salts of weak acids.
Based on the prior art, it was surprising to discover, as explained in the present application, that alkali metal alkoxides can be used as catalysts for the preparation of saccharide fatty acid polyesters, especially sucrose fatty acid polyesters, using the general procedure of Meyer et al. (i.e., lower reaction temperatures without added fatty acid metal soaps). Moreover, it was even more surprising to discover that alkali metal alkoxide catalysts provide an improved process over that of the Meyer et al. process using alkali metal catalysts. The improved method of this invention essentially eliminates or reduces the hazards (i.e., fire or explosion) associated with the use of molten alkali metals in the Meyer et al. transesterification reaction method, provides for more rapid conversion to the desired products than the Meyer et al. transesterification reaction method, and provides products having better (i.e., lighter) color characteristics than the Meyer et al. transesterification reaction method. The methods of the present invention are generally easier to use and provide better saccharide polyesters than the methods of the prior art.